The present invention is directed to an electrical connector for use with printed circuit boards. More particularly, the invention is directed to a connector of the type that uses a compression mat made out of elastomer material in order to press contact members against contact pads.
Connectors are in widespread use in the electronics industry. One class of electrical connectors employs a first mechanical support that holds first contacts and a second mechanical support that holds second contacts. In use, the first and second contacts are either pressed against one another or inserted one inside the other. One disadvantage of this class of connector is that at least one of the first and second mechanical supports must typically be mounted on a housing or other structure, and the contacts must be soldered to conductors.
In another class of connectors, printed circuit wiring extends to the edge of a printed circuit board. The edge of the printed circuit board is inserted into a fixture having contacts that engage the wiring.
In a further class of connectors, contact members on a ribbon cable are pressed against contact pads on a printed circuit board. Pressure is exerted on the back of the ribbon cable by a compression mat having compressor fingers that are aligned with the contact members and contact pads. The compression mat is clamped to the printed circuit board. The compression mat and its compressor fingers are made of elastomer materials, and the compressor fingers act somewhat as springs. When the clamping arrangement is tightened, the compressor fingers are placed under state of compression and bulge outward, like small barrels. A connector of this type is disclosed in U.S. Pat. No. 6,607,120.
Connectors of this latter type have a drawback in that the elastomer material of the compression mat has a tendency to relax after the clamping arrangement has been tightened to a desired state. The compressor fingers bulge outward and assume a shape that becomes more barrel-like with the passage of time. The relaxation of the material reduces the pressure forcing the contact members against the connector pads, and thus may lead to faulty connections.
One might consider adjusting the geometry or hardness of a compression mat in an attempt to minimize this stress relaxation. However, as the hardness of a compression mat increases, so does the actuation load that is required to compress the compressor fingers to the necessary degree. Furthermore, attempts might be made to shorten the compressor fingers in an attempt to minimize stress relaxation, but shorter, compression fingers pose reliability concerns due to assembly tolerance stack (e.g., compressor fingers that are not quite long enough but are still within tolerance may not press the contact members against the contact pads with sufficient force to ensure a reliable connection).
Another problem with conventional compression mats is that the compression fingers are prone to off-axis loading, so that one or more compressor fingers may skew to one side. This phenomenon, too, is detrimental to reliability.
The primary object of the present invention is to provide a connector which employs an elastomeric compression mat for pressing contact members against contact pads on a printed circuit board, but without the drawbacks discussed above with respect to the prior art.
A related object is to improve the reliability of a connector which employs a compression mat to force contact members against contact pads.
A further object is to provide a restrainer member that reduces the tendency of a compression mat to relax after initial compression and which also reduces skewing of the compressor fingers of a compression mat.
In accordance with one aspect of the invention, these and other objects that will become apparent in the ensuing detailed description can be attained by providing a connector that includes connector pads in a contact region on a printed circuit board and contact members that are disposed in a contact region on a first side of an insulating substrate. The contact region of the substrate is aligned with the contact region of the printed circuit board. The connector also includes a compression mat having compressor fingers that contact a second side of the substrate in alignment with the contact members on the first side, and a clamping arrangement to press the compression mat toward the printed circuit board. In order to counteract the inherent tendency of the compressor fingers to undergo stress relaxation after the compressor mat has been clamped, the connector also includes a restrainer member having holes through which the compressor fingers of the compressor mat extend.
In accordance with another aspect of the invention, a compression mat having compressor fingers is used in conjunction with a restrainer member in a method for electrically connecting pads that are disposed within a contact region on a printed circuit board to contact members that are disposed within a contact region on a first side of an insulating substrate. The method includes the step of bracing the compressor fingers with the restrainer member, which has holes through which the compressor fingers extend. The method also includes the step of placing the contact region of the substrate in a face-to-face relationship with the contract region of the printed circuit board and the step of positioning the compression mat adjacent a second side of the substrate, with the contact fingers being aligned with the contact members on the first side of the substrate. Finally, the method includes the step of pressing the compression mat toward the printed circuit board.